Week 9 Urinary System

Week 9 Urinary System

-Kidneys remove wastes from the blood (urea, uric acid, creatinine, hormones and drugs)

-Kidneys control composition and volume of blood by regulating blood ion composition (Na+, Cl-, Ca2+ and K+) and conserving/eliminating water

-Kidneys Control blood pH by regulating H+ and HCO3-

- 25-30 cm long tubes called Ureters transport urine from the kidneys to the bladder by peristalsis

-An expandable muscular organ found in the pelvic cavity called the urinary bladder provides a temporary storage reservoir for up to 800mL of urine

- Urine is transported from the bladder out of the body by the urethra

-Urethra is longer in males than in females

-Approximately one quarter of cardiac output (blood) from the heart flows through the kidneys each MINUTE

-Arterial flow ino and venous flow out of the kidneys follow similar paths

-The entire blood volume of the body is filtered by the kidneys approximately 60x per day

-The functional unit of the kidney is the nephron

-The nephron makes urine

-Each kidney contains approximately 1 million nephrons

-Each nephron consists of a tubular component and blood vessels

- The three processes of Urine formation are Glomerular filtration, Tubular reabsorption and Tubular secretion

- In glomerular filtration ALL blood components, except for blood cells and most proteins, will pass through the (porous) glomerulus and will be collected as filtrate in the Bowman's Capsule

-Glomerular filtration is efficient because the filtration membrane (lining of capillaries and nephron) is thin and very permeable

-Glomerular filtration is efficient because the glomerular capillaries have a large surface area

-Glomerular filtration is efficient because blood is filtered at high pressure

-Glomerular filtration is when blood enters the afferent arteriole and flows into the glomerulus where filterable blood components, such as water and nitrogenous waste, will move towards the inside of the glomerulus, and nonfilterable components, such as cells and serum albumins, will exit via the efferent arteriole. These filterable components accumulate in the glomerulus to form the glomerular filtrate.

-Glomerular filtration is a passive process

-Tubular reabsorption is when molecules and ions will be reabsorbed into the circulatory system. The fluid passes through the components of the nephron (the proximal/distal convoluted tubules, loop of Henle, the collecting duct) as water and ions are removed as the fluid osmolarity (ion concentration) changes. In the collecting duct, secretion will occur before the fluid leaves the ureter in the form of urine.

-Tubular reabsorption refers to the return of most of the filtered water and many of the filtered solutes to the bloodstream from the tubules

-During Tubular reabsorption approximately 99% of the water of the filtrate is returned to the blood stream and 1% is excreted as urine

-During Tubular reabsorption ALL nutrients are reabsorbed and electrolytes are reabsorbed as needed to maintain homeostasis

-During Tubular secretion some substances are actively secreted from blood into tubules for excretion (opposite of reabsorption)

-Tubular secretion is important for eliminating undesirable substances such as creatinine, urea and uric acid

-Tubular secretion is important for controlling blood pH (H+)

-Tubular secretion is important for ridding the body of excess potassium ions (K+)

-Tubular secretion is important for disposing of substances not already in the filtrate

-The nephron is comprised of the proximal convoluted tubule, the descending Loop of Henle, the ascending Loop of Henle, the Distal convoluted tubule and the Collecting duct

- Urine is mainly composed of water that has not been reabsorbed, which is the way in which the body lowers blood volume, by increasing the amount of water that becomes urine instead of becoming reabsorbed. The other main component of urine is urea, a highly soluble molecule composed of ammonia and carbon dioxide, and provides a way for nitrogen (found in ammonia) to be removed from the body. Urine also contains many salts and other waste components. Red blood cells and sugar are not normally found in urine but may indicate glomerulus injury and diabetes mellitus respectively.

-The descending loop of Henle only allows for reabsorption of water by osmosis, not salt

-The ascending loop of Henle is where Na+ ions are actively pumped out and Cl- ions passively follow them

-The ascending loop of Henle is impermeable to water

-The two most important hormones regulating urine volume and composition are ADH and Aldosterone

- ADH is produced in the hypothalamus and is released by the posterior pituitary gland

-When you are thirsty ADH action is characterized by increased blood volume, decreased blood solute concentration, decreased urine volume and increased urine solute concentration

-When you have had too much water the absence of ADH is characterized by a decrease in blood volume, an increase in the concentration of blood solutes, an increase in urine volume and a decrease in urine solute concentration

-Aldosterone helps regulate Na+, K+ and H+ homeostasis and blood pressure

-Stimulation of aldosterone secretion from the adrenal cortex is due to a decrease in plasma sodium, an increase in plasma potassium or a decrease in blood volume

-A decrease in blood pressure causes juxtaglomerular cells to secrete the enzyme renin into the blood

-Renin become angiotensin 2 and subsequently aldosterone

-Aldosterone causes the reabsorption of sodium and chloride ions which indirectly causes water reabsoprtion and an increase in blood volume

-Aldosterone causes secretion of potassium and hydrogen ions in the collecting ducts

-Urine is 95% water and 5% solutes

-The solutes in urine are comprised of nitrogenous wastes, inorganic ions and urochrome

-Nitrogenous wastes in urine are urea, uric acid and creatinine

-Inorganic ions in urine are sodium, potassium, phosphate and sulfate ions AND Calcium, magnesium and bicarbonate ions

-Urochrome is responsible for the colour of urine

-A normal volume of urine voided per day is 1-2 liters

-Less than 30mL of urine per hour could indicate kidney failure

-Variations in solute concentration of urine are assessed by specific gravity (SG)

-Specific gravity of normal urine ranges from 1.008 - 1.030 g/ml

-Normal urine is usually slight acidic with a pH of 6 but can vary from 4.5-8

-Variation of urine pH is closely related to diet where high protein diets decrease urine pH and a diet high in vegetables will increase pH

-Other factors like fasting, high altitude and exercise can influence urinary pH

-Anuria is a total absence of urine and could indicate an obstruction of the urinary tract

-Oligouria is very little of scanty urine which could indicate acute renal failure or dehydration

-Polyuria is excess urine output and could indicate either diabetes mellitus or insipidus

- Dysuria is painful urination and could indicate a UTI or kidney stones

-Hematuria is the presence of blood in the urine and could indicate urinary stones, kidney disease, glomerular infection, bladder cancer, contamination of menstrual blood

-Glycosuria is the presence of glucose in the urine and could indicate diabetes mellitus or ineffective glucose reabsorption

-Pyuria is the presence of leucocytes and pus in the urine which could indicate an infection of the urinary or reproductive tract in males

-Albuminuria is the presence of albumin in the urine which could indicate kidney disease, high blood pressure, pregnancy

-Acetonuria is the presence of acetone and ketones in urine which could indicate diabetes mellitus 

-Biliuria is the presence of bilirubin in the urine which could indicate liver disease or obstruction of bile ducts

- The urinary bladder is an expandable sack made of smooth muscle that has a 0-500mL capacity

-The smooth muscle that makes up the urinary bladder is called the detrusor muscle

-Urine enters the urinary bladder via ureter and exits via the urethra, which is guarded by two sphinters

-The male urethra is longer than the female urethra

-The internal urethral sphincter of the urinary bladder is involuntary while the external urethral sphincter is voluntary

-When urine fills the urinary bladder it stretches, triggering stretch receptors to transmit a nerve impulse to the spinal cord/cerebral cortex, this then triggers a spinal reflex called the micturition reflex

-Parasympathetic impulses from the micturition center travel to the urinary bladder and cause the detrusor muscle to contract and the internal sphincter to relax

-The micturition center also inhibits the motor neurons that keep the external sphincter closed, causing it to relax and urine to flow out

-The external sphincter can voluntarily close by overriding the parasympathetic neurons and voluntarily contract, closing the sphincter

-If the external sphincter is closed voluntarily this will cause the micurition reflex to subside, but only for time and then it will return as a stronger impulse.